Electron beam source and the use of the same

A method for forming a three-dimensional article through successively depositing individual layers of powder material that are fused together so as to form the article, the method comprising the steps of:

• emitting an electron beam, via at least one electron beam source and for at least one of heating or fusing the powder material, the at least one electron beam source comprising a cathode, an anode, and a grid between the cathode and anode, wherein the cathode is having a base and a protrusion with sidewalls and a top surface, the base having a base surface which is essentially in parallel with the top surface, the base surface and the top surface are essentially flat and facing towards the anode, the base surface and the top surface are arranged at a predetermined distance from each other, the base is larger than the protrusion, the sidewalls are essentially perpendicular to the base surface and the top surface, and
• changing an applied voltage to the grid for switching a spot size of the electron beam on a target surface between at least a first spot size corresponding to emission from the top surface of the cathode only and to a second spot size corresponding to emission from the top surface and the base surface of the cathode.

A computer program product comprising at least one non-transitory computer-readable storage medium having computer-readable program code portions embodied therein, the computer-readable program code portions comprising at least one executable portion configured for:

• controlling an electron beam source when formation of a three-dimensional article, the electron beam source emitting an electron beam for at least one of heating or fusing individual layers of a powder material together so as to form the three-dimensional article, the electron beam source comprising a cathode, an anode, and a grid between the cathode and anode wherein the cathode is having a base and a protrusion with sidewalls and a top surface, the base and the top surface are essentially in parallel with each other, essentially flat and facing towards the anode, the base and the top surface are arranged at a predetermined distance from each other, the base is larger than the top surface, the sidewalls are essentially perpendicular to the base and the top surface;
• and
• changing an applied voltage to the grid for switching a spot size of the electron beam on a target surface between at least a first a first spot size corresponding to emission from the top surface of the cathode only and to a second spot size corresponding to emission from the top surface and the base of the cathode.